For purification of water quality of swimming pools installed in sports facilities, theme parks, etc., purification of water quality of water tanks installed in aquariums, and purification of the atmosphere, a purification technique of an adsorption system using activated carbon, a purification technique of a sterilization system using hypochlorous acid, etc., have been used.
However, the adsorption system using activated carbon has a problem that replacement of activated carbon is performed frequently when a large quantity is purified.
Moreover, the sterilization system using hypochlorous acid has a problem of odor, skin irritation, etc., due to chlorine residues.
Furthermore, it is difficult to remove fine organic pollutants using the above-described purification techniques.
Therefore, a purification technique using a photocatalyst is proposed as a purification technique that is harmless to human bodies, has less frequent replacements of a filter material, and is capable of removing fine organic pollutants (see, for example, Japanese Registered Utility Model No. 3044655, and Japanese Patent Application Laid-Open (JP-A) Nos. 10-85606, 2006-130365, 2001-293071, and 2007-167784). In the proposed techniques, purification is performed by applying ultraviolet rays to a photocatalyst that is titanium dioxide or optionally a carrier to which titanium oxide that is a photocatalyst is born.
However, the proposed technique has a problem that it is difficult for ultraviolet rays to reach the photocatalyst far from a light source of ultraviolet rays and therefore purification performance is not sufficient.